Class II Springs to the Archwire
Drs. Miller, Tieu, and Flores-Mir's article titled "Incisor inclination changes produced
by two compliance-free Class II correction protocols for the treatment of mild to
moderate Class II malocclusions" is in the online version of the Angle Orthodontist.
It is based on Dr. Bob Miller's clinical study.
He compared 36 Class II patients treated in one phase with Forsus to the archwire
in a full edgewise appliance to 38 similar Class II patients treated in two phases
with Xbow followed by a full edgewise appliance. The Forsus to the archwire group
was finished in an average of 30.2 months (between records). The Xbow group was finished
in an average of 24.2 months (between records), which included a 4 to 6 month rest period
to allow for relapse. The two phase Xbow patients were completed 6 months faster on
average than the one phase Forsus to the archwire patients (time between records).
The Forsus to the archwire group had full braces for an average of 26.75 months. The
Xbow group had full braces for an average of 16.68 months, or 10 fewer months.
There was no significant difference in the lower incisor to mandibular plane angle
between the two groups. The Xbow patients ended up with lower incisors at an average
of 100 degrees to mandibular plane which is considered a reasonable compromise for
non-extraction Class II compensation.
Editor's note: Longer treatment time with Forsus to the archwire is due to dealing
with the spring side effects late in treatment such as posterior openbite and
buccal flaring of the upper molars. The greater the correction the greater the
side effects and the longer it takes to deal with them.
There is no buccal flaring of the upper molars with Xbow.
Much of the posterior openbite and proclination of the lower incisors rebound
before full braces are placed.
The side-effects of Forsus on the archwire are especially problematic when the spring is used unilaterally late in treatment.
The unilateral posterior openbite and anterior canting requires prolonged treatment with good elasitc cooperation to recover.
We do not see the anterior canting when the spring is used unilaterally on a Xbow.
The fact that the first bicuspids are already Class I after Xbow therapy reduces the time in phase two braces
and the need for side-effect correction with elastics.
I use the same principles when using the Forsus device with a full edgewise appliance as I do with Xbow.
Use the 22mm Direct Pushrod distal to the lower first bicuspid instead of the canine, if possible.
This keeps the Forsus device more compact and moves it distal to the anterior curvature of the arch,
preventing the need for rod adjustments. It also keeps the spring distal to the Obicularis Oris muscle, preventing sores.
The only difference is you cannot fully compress the spring with an edgewise appliance if you use a bracket as the anterior stop.
If you do be prepared to rebond the bracket. Don't forget to steel tie the first bicuspids.
Reactivate the springs with crimpable stops on the rods or use longer rods.
Dr. Bob Miller taught us to hook up the pushrod using an Alastic KX module to activate the spring but at the same time remove
the force from the canine or first bicuspid bracket. This also negates the need to cinch the distal end of the arch wire.
Place the springs and pushrods as you would normally but don't close the loop yet. Make the pushrod adjustments
leaving 1mm of play in the spring, remove the pushrod, pre-stretch a KX-1 module, place the KX module on the pushrod,
place the pushrod on the archwire, close the pushrod loop, hook the KX module to the first molar hook using floss
and a floss threader over the second bicuspid bracket and down between the second bicuspid and first molar,
then place the pushrod in the spring. This completely activates the spring without debonding the canine or first bicuspid bracket.
If we place the 22 mm or 25 mm pushrod distal to the first bicuspid we use a KX-1 module.
We also use a KX-1 module distal to the canine in a bicuspid extraction case.
Alastic KX-1 module placed with floss threader
Alastic KX-1 module and lingual tuck-in pushrod adjustment on 25mm rod
Alastic KX-1 module hook-up distal to canine (severe Class II, patient decided against mandibular advancement surgery after preparation)
Alastic KX-1 Module hook-up distal to first bicuspid
Alastic KX-1 Module hook-up distal to canine (bicuspid extraction) with a 22 mm pushrod.
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